Plastic lids for large containers are of course well known and in extensive use. However, one limitation to their use is the tendency for the plastic lids, being somewhat flexible, to pop off of a container when it is dropped. This is especially a problem in containers of the size of half a gallon or more, so that, at the present time, plastic lids for large containers are usually retained in place with a wire ring about the periphery thereof. This of course contributes significantly to the cost of the container and inconvenience of use.
Another solution for the problem of pop-off of plastic lids when containers are dropped is illustrated in Bordner U.S. Pat. No. 4,718,571. There, a lower portion of the skirt of the lid is folded upwardly into engagement with the lip of the container. The system is removed by the tearing of circumferential "parting groove" or line of weakness 60 (FIG. 4A).
However, it has been found that when a larger container of about a half gallon or more is dropped, a shock wave generated in the liquid contents can strike the lid with sufficient force to break circumferential lines of tearing weakness. Thus, the Bordner design has limitations in its drop strength. Similarly, other designs which utilize circumferential tear strips, such as the design of Von Holdt U.S. Pat. No. 4,735,337, can exhibit similar limitations.
By this invention, a snap-on lid for a container, which lid is typically made of flexible plastic, may be provided with significantly increased drop strength, when compared with analogous prior art designs. Also there may be less need for an external retaining wire ring to hold the lid on the container lip. Thus, since the lid may be molded of plastic in a manner similar to other prior art lid designs at little or no increase of cost, a significant improvement and cost saving is achieved.
Nevertheless, despite the high drop strength of the lid of this invention, it can be opened with ease, typically having a level of flexibility to facilitate the manual removal thereof by people without strong hands.